Ball mill



JunlS, 1965 Filed Dec. 18, 1962 E. c. MILLER 3,189,285

BALL MILL 2 Sheets-Sheet 1 FIG. I

EARLE C. MILLER INVENTOR June 15, 1965 E. c. MlLLER 3,

- BALL MILL Filed Dec. 18, 1962 Zfieets-Sheet 2 FIG. 2

EARLE C. MILLER INVENTOR ZZ MYK sl 1" United States Patent M 3,189,285 BALL MILL Earle C. Miller, Worcester, Mass, assigner to Riley Stoker Corporation, Worcester, Mass a corporation of Massachusetts Filed Dec. 18, 1962, Ser. No. 245,547 6 -Claims. (Cl. 241-17 1} This invention relates to a ball mill and, more particularly, to apparatus arranged to pulverize solid fuels and the like.

In the pulverization of coal, the ball mill occupies an outstanding place because of its basically simple and rugged construction and its relatively low cost of operation. It has, however, suiiered from a number of deficiencies. One of these lies in the fact that the capacity of such a mill depends, to a great extent, on the amount of air which can be passed through the mill; this amount has been limited in the known mills by the fact that the unpulverized fuel and air enter a hollow trunnion at one end of the mill and the pulverized fuel and air leave at the other end of the mill. Furthermore, the operator of the mill has an irreconcilable choice to make between providing air sufiicient in amount to satisfy the load on the mill and providing sufficient air to dry the fuel before it anrives at themill and to carry the powdered coal through the ducts leading to the burners. The amounts of air may be vastly different, so that the mill must operate at less than its optimum efiiciency. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a ball mill in which the capacity for pulverization for a given size is greatly increased.

Another object of the invention is the provision of a ball mill in which provision is made for making use of optimum air flow through the mill at a given load while, at the same time, maintaining the optimum air flow for proper drying of the fuel before it arrives at the mill and maintaining adequate air to carry the pulverized coal to the burners without clogging of the pipes.

A further object of the present invention is the provision of a ball mill having outstanding capacity and capable of maintaining the most effective air flow.

It is another object of the instant invention to provide an elongated ball mill in which unpulverized fuel may be introduced at both ends of the mill.

It is a further object of the invention to provide a ball mill in which at low loads small amounts of air may pass through the ball mill and yet no difiiculty is experienced in conveying pulverized material through the ducting and piping associated with the mill.

With these and other objects in view as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by referenceto one of its structural forms, as illustrated by the accompanying drawings in which:

FIG. 1 is a vertical longitudinal sectional view of a ball mill embodying the principles of the present invention,

FIG. 2 is an end elevational view of the mill, and

FIG. 3 is a vertical sectional view of the mill taken on the line III-Ill of FIG. 1.

Referring to the drawings, the ball mill, indicated generally by the reference numeral 10, is shown in use with a steam generating unit 11 having burners 12. The burners are connected to the mill by means of pipes 13. The ball mill is mounted on concrete abutments 14 and 15 extending upwardly from a concrete foundation 16. The mill consists of a tubular main body 17 having end plates 13 mg walls of the duct 32 and the duct 43. The duct 32 permit by-passing of air around the pulverizer after the air feeder 52 and crusher-dryer 53 is associated with the trunthe duct 32 and carries a pressure reading to the control Patented June 115, i965 and 19 from which extend co-axial tubular trunnions 21 and 22. Located within the main body is a load 23 of material to be pulverized along with pulverizing balls of iron or the like. This material may be coal, for instance and, due to the rotation of the main body, lies with an upwardly-facing surface 24 which lies at a substantial angle to the horizontal. Across the trunnion 21 lies a dividing plate 25 which extends in a plane parallel to the axis of the trunnion 21 and the main body 17 and is spaced and parallel to the surface 24 of the load 23. The trunnion 22 is provided with a similar dividing plate 26. The dividing plate 25 is mounted in a sleeve 27 mounted Within the trunnion 21, while a similar sleeve 28 is provided within tl e trunnion 22 to hold the plate 26. This sleeve arrangement permits the plates 25 and 26 to be readily removed and permits adjustment for angularity. The ball mill is provided with a suitable wear-resistant liner in the usual way.

The dividing plate 25 divides the trunnion 21 into an inlet portion 29 and an outlet portion 31. Extending from the inlet portion 29 is a duct 32 leading to a crusher-dryer 33. The crusher is connected by a duct 34 to a feeder 35 and by a branch duct 36 leading to a main duct 37 which, in turn, is connected through a. fan 38 to the air plenum chamber around the burners 12. The chamber is connected by a duct 41 to an air preheater (not shown). The bottom of the duct 32 is connected by a pipe 42 to the operating floor of the apparatus for the introduction of new grinding balls into the pulverizer as the old ones wear out.

The outlet portion 31 is connected by a duct 43 to a classifier 44. This classifier is of the type using a row of horizontal tubes 45 which are arranged at a sharp angle to the flow of gas. A return duct 46 receives coarse particles from the underside of the row of pipes 45 and returns them to the bottom of the duct 32 close to its attachment to the inlet portion 29. A stub duct 47 connects the fachas an opening with fixed vanes 48 mounted in it, the opening leading into the duct 47. The wall of the duct 43 is provided with an opening having an adjustable vane 4?, the opening leading from the duct 47 into the duct 43 to and fuel leave the crusher-dryer 33. The ducts 32 and 43 are very closely related and are provided with a bellows 51 which prevents the transmission of vibrations into the upper piping of the unit. A similar arrangement of nion 22 at the other end of the mill. A classifier 54 with return ducts and a by-pass is provided at this end of the mill also. Extending through the outlet space 31 into the mill is a pipe 55 leading to a level sensing device 56. The pipe 55 extends through the wall of the duct 32 and is connected by a line 57 to a control box 58. A similar pipe 59 extends through the trunnion 22, is provided with a level sensing device 61 and is connected by a line 62 to a control box 63. A line 64 is connected to the interior of box 58. A similar line 65 opens at one end into the corresponding duct associated with the trunnion 22 and is connected to the control box 63. The control box 58, is in turn, connected through a line 66 to the feeder 35 to control the rate of feeder fuel into the system, while a similar line 67 extends from the control box 63 to the feeder 52.

An air sealing system 6%, furnished with pressure air by fans 6@ and '71, leads to the crusher-dryers 33 and 53 and the feeders 35 and 52 to prevent coal dust from entering the operating room of the steam generating unit. A large ring gear 72 is mounted on the exterior of the main body 17 of the mill and is used to drive it.

The operation of the apparatus will now be readily understood in view of the above description. Fuel enters the system through the feeder 35 and 52, while heated air enters through the main duct 37. They meet under the feeders 35 and 52 and together pass through the crusher-dryers 33 and 53, where the rough coal is subjected to a crushing action and the turbulence stimulated in the apparatus causes a thorough mixing of the fuel and warm air to dry the coal. The crusher-dryer 33 releases the mixture of primary air and crushed fuel down the duct 32 Where it passes through the inlet opening 29 into the ball mill and joins the load 23. Because of its weight and the nature of the centrifugal action as the direction of air and fuel flow down the duct 32 vertically and horizontally through the inlet portion 29, the coal falls directly into the load and stays in the bottom part of the main body of the mill 17. The level of the load is maintained at a desired value by the level sensing devices 56 and 61 which transmit a signal back to the control box 58. This is combined with the signal in the duct 32. to control the rate of feed. Now, the primary air which arrives with the fuel continues upwardly over the top of the load Where it meets a similar flow of air arriving from the other end of the mill. The two strike one another and are reversed in the center of the mill and then are forced to move horizontally backward. The air from trunnion 21 passes through the outlet portion 31 above the divider plate 25. This air, of course, contains a certain amount of fine pulverized coal and, as it passes upwardly through the duct 43, the mixture strikes the row of tubes 45. The coarse particles are returned to the mill through the duct 46, while the air and the fine particles continue up the pipes 13 to the burners 12 where they provide combustion in the steam generating unit 11. It can be seen, then, that, by causing the fuel and air to enter and leave through the same end of the ball mill, the ball mill can be provided with entrances at either end so that the length of the ball mill can be greatly increased. It has long been known, of course, that a certain minimum of flow of air must be maintained in the pipes 13 leading to the burners, otherwise the fuel settles out. It is also a known fact that the fuel which is removed from the storage capacity of the ball mill is in direct proportion to the flow of air therethrough. The problem arises as to how to maintain adequate flow of air through the pipes while still reducing the air in the ball mill at low loads. This is accomplished :by the present invention by providing a by-pass means through the duct 47. A proportion of the air passing downwardly through the duct 32 i moved sideways and flows sideways over the vanes 48, while the fuel continues on downwardly into the ball mill. The air that passes over the vanes 48 also passes over the vane 49 which regulates the amount of such by-passing. This bypassed air joins the air and pulverized coal which is arriving upwardly through the duct 43 and together they pass through the classifier 44 and upwardly into the pipe 13. The flow of air through the pipe 13, therefore, is much greater than flows through the mill, so that both of the necessary restrictions on mill operation and proper drying and burner pipe flow are readily arranged.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent,

l. A ball mill, comprising (a) a horizontal tubular main body,

(b) a tubular trunnion extending co-axially from each end of the main body,

(c) bearing means supporting the trunnions to permit rotation of the main body about its axis,

(d) means driving the main body to produce the said rotation,

(e) a dividing wall extending across one of the trunnion and dividing it into an inlet and an outlet portion,

(f) means introducing solid fuel into the inlet portion of the trunnion,

(g) and means removing pulverized fuel and air from the main body through the outlet portion.

2. A ball mill, comprising (a) a horizontal tubular main body,

(b) a tubular trunnion extending co-axially from each end of the main body,

(0) bearing means supporting the trunnions to permit rotation of the main body about its axis,

(d) means driving the main body to produce the said rotation,

(e) a driving wall extending across one of the trunnions and lying substantially in a plane parallel to the axis of the main body, the wall dividing the bore of the trunnion into an inlet and an outlet portion,

(f) means introducing solid fuel into the inlet portion of the trunnion, and

(g) means removing pulverized fuel and air from the main body through the outlet portion.

3. A ball mill, comprising (a) a horizontal tubular main body,

(b) a tubular trunnion extending co-axially from each end of the main body,

(0) bearing means supporting the trunnions to permit rotation of the main body about its axis,

(d) means driving the main body to produce the said rotation,

(e) a dividing wall extending across one of the trunnions and dividing it into an inlet and an outlet portion, both portions having a duct connected thereto,

(f) means introducing solid fuel into the inlet portion of the trunnion,

(g) means removing pulverized fuel and air from the main body through the outlet portion,

(h) a by-pass connecting the inlet and the outlet ducts,

and

(i) means for adjusting the amount of air which is shunted through the by-pass.

4. A ball mill, comprising (a) a horizontal tubular main body,

(b) a tubular trunnion extending co-axially from each end of the main body,

(0) bearing means supporting the trunnions to permit rotation of the main body about its axis,

(d) means driving the main body to produce the said rotation and to cause the load of grinding elements and fuel to occupy a position in the main body such that the surface of the load lines in a general plane which is substantially inclined to the horizontal,

(e) a dividing Wall extending across one of the trunnions and dividing it into an inlet and an outlet portion,

(f) means introducing solid fuel into the inlet portion of the trunnion, and

(g) means removing pulverized fuel and air from the main body through the outlet portion, the dividing wall extending across the trunnion in a plane which is generally parallel to the surface of the load.

5. A ball mill, comprising (a) a horizontal tubular main body,

(b) a tubular trunnion extending co-axially from each end of the main body,

(c) bearing means supporting the trunnions to permit rotation of the main body about its axis,

((1) means driving the main body to produce the said rotation,

(e) a dividing wall extending across one of the trunnions and lying in a plane parallel to the axis of the main body, the wall dividing the bore of the trunnion into an inlet and an outlet portion,

(f) means introducing solid fuel into the inlet portion of the trunnion,

(g) means removing pulverized fuel and air from the main body through the outlet portion,

(h) a duct connected to the inlet portion,

(i) a duct connected to the outlet portion,

(j) a by-pass joining the two ducts, and

(k) means for adjusting the amount of air which is 10 shunted through the by-pass.

6. A ball mill, comprising (a) a horizontal tubular main body,

(b) a tubular trunnion extending co-axially from each end of the main body,

(c) bearing means supporting the trunnions to permit rotation of the main body about its axis,

(d) means driving the main body to produce the said rotation,

(e) a dividing Wall extending across each of the trunnions in plane parallel to the axis and dividing it into an inlet and an outlet portion,

(5) means introducing solid fuel into the inlet portion of the trunnion, and

(g) means removing pulverized fuel and air from the main body through the outlet portion.

Reierenees Qited by the Examiner UNITED STATES PATENTS 2,109,449 3/38 Harman 24134 2,174,630 10/39 Hardinge 241-52 XR 2,256,841 9/41 Hardinge 24154 XR 2,285,429 6/42 Frisch 241--54 2,316,875 4/43 Laboulas 241-34 3,032,280 5/62 Whitney et al 241-471 XR 3,078,048 2/63 Russel et a1 24152 XR 29 I. SPENCER OVERHOLSER, Primary Examiner. 

1. A BALL MILL, COMPRISING (A) A HORIZONTAL TUBULAR MAIN BODY, (B) A TUBULAR TRUNION EXTENDING CO-AXIALLY FROM EACH END OF THE MAIN BODY, (C) BEARING MEANS SUPPORTING THE TRUNNIONS TO PERMIT ROTATION OF THE MAIN BODY ABOUT ITS AXIS, (D) MEANS DRIVING THE MAIN BODY TO PRODUCE THE SAID ROTATION, (E) A DIVIDING WALL EXTENDING ACROSS ONE OF THE TRUNNIONS AND DIVIDING IT INTO AN INLET AND AN OUTLET PORTION, (F) MEANS INTRODUCING SOLID FUEL INTO THE INLET PORTION OF THE TRUNNION, (G) AND MEANS REMOVING PULVERIZED FUEL AND AIR FROM THE MAIN BODY THROUGH THE OUTLET PORTION. 